Polyoxyalkylene-modified polysiloxane compositions have heretofore been synthesized by a hydrosilylation reaction between an organohydrogenpolysiloxane bearing the silicon-bonded hydrogen group and a polyoxyalkylene having an allyl ether group in terminal position. However, the polyoxyalkylene-modified polysiloxane compositions obtained in this manner have been prone to generate odor with elapsed time, and it has been quite difficult to achieve a scent-free condition when they are used in cosmetic applications, e.g., for hair cosmetics and skin cosmetics, which has placed limitations on their quantity of incorporation and their applications.
This odor is thought to be due to an internal migration by the terminal double bond in the allyl ether group-containing polyoxyalkylene that occurs during the hydrosilylation reaction and that results in the secondary production of the isomeric propenyl ether group-containing polyoxyalkylene, which then undergoes gradual hydrolysis due to the presence of moisture and trace acid in the system to produce odor-causing propionaldehyde.
In order to address this, a method has been introduced in which hydrolysis is forcibly performed after the hydrosilylation reaction by reacting the propenyl ether with an acidic aqueous solution or an acidic substance in order to produce the odor-causing propionaldehyde, which is subsequently removed (refer to Patent Document 1). A method has also been introduced in which the propenyl ether group-containing polyoxyalkylene is degraded using an acidic substance and a lower alcohol in place of water; an adduct is formed between the propionaldehyde and the lower alcohol; and these are thereafter removed (refer to Patent Document 2). However, in both of these methods only mineral acids such as hydrochloric acid, sulfuric acid, or nitric acid, organic acids such as formic acid or acetic acid, or Lewis acids are provided as examples of the acidic substance. A problem with these acids has been that during the hydrolysis reaction they cleave the carbon-oxygen bond in the polyoxyalkylene moiety as well as the silicon-oxygen bond in the organopolysiloxane moiety. In addition, excess amounts of acid and water or alcohol are required in order to drive the hydrolysis reaction to completion, and these must then be removed by volatilization. A problem here is that this promotes the previously indicated acid-mediated cleavage of the carbon-oxygen bond and silicon-oxygen bond.
In order to solve the problems posed by these acids, a method has been introduced in which the hydrosilylation reaction is followed by treatment in the presence of a solid acid (refer to Patent Document 3). However, contact with the propenyl ether group-containing polyoxyalkylene is not adequate when a solid acid is used, resulting in inadequate hydrolysis and the occurrence of odor generation with elapsed time. In addition, when the amount used has been increased in order to boost the efficiency, problems have arisen such as an impaired workability due to escape during filtration, an impaired workability due to clogging during the filtration process, and a tendency for discoloration to occur. Furthermore, solid acids are also known to function as polycondensation reaction catalysts, and as a result the previously indicated acid-mediated carbon-oxygen bond and silicon-oxygen bond cleavage still similarly occurs. Moreover, solid acids are insoluble in both water and organic solvents, which complicates the ensuing washing step.    [Patent Document 1] JP 02-302438 A (JP 07-091389 B)    [Patent Document 2] JP 2004-189959 A (JP 4,064,223 B)    [Patent Document 3] WO 2004/046226